Today at Atelier Kaz - ex-Honda R&D, F1, Indy/CART engineer

Helping one owner who bought GROM BT3 recently but having problem.


Probably very limited number of GROM BT3 users in Europe but hoping to get some feedback through here and on NSX Prime.
Then, planning to share this at the GROM Audio US Forum so that someone at GROM can look into this.

Please note that this issue only occurs if you have the European spec OEM head unit with GROM BT3.

JDM and Acura OEM Head Unit works fine with BT3.

Another device such as GROM USB3 works fine with the European/JDM/Acura OEM head unit.


If you happen to have the European spec OEM head unit with GROM BT3 on your NSX and have no issues, I'll appreciate if you can share the following info.
Q1: When did you get the BT3 unit? This may help in finding out the firmware version.
Q2: Did you reprogram the firmware and if so, which version?
Q3: Android, iOS or other OS device connected over Bluetooth?
(Most likely, not related to OS because the issue happens even with the device directly connected at the AUX port.)
Q4: Any other issues experienced?


Issue:
With the European spec NSX OEM head unit, GROM BT3 will no longer play the device audio if you change the head unit mode or switch off the unit.
This is regardless of whether connected through the bluetooth or directly at the AUX port using the dedicated cable.

Key findings:
While in CD mode with this issue, changing the volume setting on the head unit has no effect.

In fact, almost no white noise through the speakers despite changing the head unit volume to Max level.
Was in very quiet bench testing environment and with this issue, almost felt as if the BT3 was in muted mode or something disabling any audio output.

One can only play about 0.1sec of audio from the BT3 immediately after selecting the CD mode and then nothing.
Not even white noise.
Every time when you select the CD mode, the same 0.1sec audio and then muted.

Despite the issue, the bluetooth connection was always maintained, i.e. the BT3 and the bluetooth kept paired and recognised each others.

At least one owner in UK managed to make it work (European spec OEM head unit + GROM BT3) after spending 2 days as initially, the BT3 didn't work.
Not confirmed yet whether he tested again after power cycling.

Observation:
After successfuly making the BT3 to wotk with the European spec head unit, changing the mode from CD to Radio, switching Off the radio, turning the IGSW into P0 Off will all trigger this issue.

Same result for not only the device wirelessly connected over the Bluetooth but also even the one directly connected via AUX port cable.

The only way to make it work again is to perform the 'reset' procedure on the BT3.
To perform the 'reset', you'll need to press 'Scan' or 'Repeat' button multiple times immediately after selecting the CD mode.

This will force you to pair the Bluetooth device every time when you perform the 'reset'.
Not practical while you are driving or everytime when you park the car.

As in the BT3 user manual, waited long enough before start playing any music.
In fact, didn't even open the music App for more than 5min.

MBUS is based on sequence of multiple pulse width command signal.
Since another model USB3 does work with European spec head unit, seems as if BT3 went into different status or muted when the head unit mode was changed.

With the JDM and Acura unit, when mode selector is pressed, it will cycle through as follows;
AM -> FM -> CD -> back to AM

With the European spec;
UKW (FM) -> CD -> LW -> MW -> back to UKW

The mode selection difference described above could be the key in solving this issue.
However, another GROM device - USB3 does work with the European spec head unit even with the difference in selecting the mode.

Although tested in logical steps, I could be doing something wrong so any advices welcome.
Have electronics background and installed other GROM device - USB3 several times on NSX so not an amateur.

The GROM BT3 unit was purchased by another owner and not mine.
GROM kindly replaced the original BT3 unit with another one for the owner.

Since both BT3 units are not mine, decided not to connect the oscilloscope to check the state of MBUS.
Don't want causing any damages to something not owned by me.


Test condition:
Tested 2 x GROM BT3 + 2 x HON92 adaptor loom but exactly the same issue.

Tested using 3 x European spec OEM head unit, 1 x JDM OEM head unit.

One of the European unit was used for testing both BT3 units.

All of the European units showed exactly the same issue for both BT3 units.

JDM unit worked fine for both BT3 units.

The CD function on all of the head units mentioned above were tested using the USA SPEC PA11-HON and worked fine.

Didn't have Acura audio head unit but enough BT3 usage feedback on the NSX Prime.

Even with the issue, the Bluetooth link to the device maintained.

Only tested with the Android devices.

On purposely used different Android version although ready knew not related as all devices worked fine with JDM unit.

Used phones from Samsung and Google Pixel.

Used Pixel tablet as well.

All of them showed the same result if used with European spec head unit.

Not tested using iOS but should not matter.

Even the device directly connected through AUX port loom showed the same issue.


Tried all of the previous firmware but still the same result.







Testing with JDM head unit.









Didn't take photo of the 1st BT3 unit but these are the ones from the 2nd unit.

Only FAT based file system accepted for GROM device so tried both the FAT16 and FAT32 for firmware programming.


Kaz